High temperatures and humidity don't just affect your walls, ceilings and floors in your bathroom and can potentially cause mold to form. It can also affect the things that you might commonly store in the bathroom as well!
Books and Magazines: Taking a nice relaxing bath seems incomplete without a good read. However those books and magazines can absorb moisture which causes damage to the pages. Leaving a book in the bathroom for even just a day can wrinkle the pages and damage the bindings.
Medicines and Vitamins: It seems logical that you would store your medicines in your bathroom medicine cabinet. If you read the information on your medicine bottles you'll know that pills should be stored in a cool and dry location. The bathroom's moisture alone can cause problems, even if you take only cold showers and keep the room at the right temperature.
Perfume: Bathroom humidity can get inside the bottle causing perfumes to lose their potency.
Nail Polish: The average bottle of nail polish can last up to two years (if shaken regularly). The life span will be greatly reduced if you leave it in a room with fluctuating temperature and humidity.
Jewelry: Oxidization, a natural process that is sped up by water and humidity, can tarnish and discolour jewelry, even on new accessories.
Spare Razor Blades: Moisture and steam from showers and baths can dull the blades and promote rust, making them ineffective and potentially dangerous.
Linens: I know you're saying, "but you need towels in a bathroom!" Of course you do, but if you fold and store them while still damp you're encouraging mildew.